The long-term goals are characterization of superantigens (SAgs) causation of diseases. SAgs cause toxic shock syndrome (TSS). However, it is our hypothesis that SAgs contribute to other illnesses. We theorize SAgs produced by emerging strains of methicillin resistant Staphylococcus aureus (MRSA) (USA 200, 300, and 400) contribute to necrotizing pneumonia (NP), pulmonary TSS, and endocarditis. We also hypothesize there may be adjuvant uses for SAgs, when toxicity is eliminated. We plan two specific aims: Aim 1: To characterize adjuvant activities of non-lethal SAg toxoids that amplify antibody production when administered intravenously or mucosally, as a consequence of their abilities to interact with CD40. We provide evidence that SAgs contain a domain that facilitates mucosal penetration, independent of superantigenicity, and that amplifies immune responses;both activities result from interaction with the immune co-stimulatory molecule CD40. Specific aim 1a. To prepare mutants in the dodecapeptide domain of SAgs, TSS toxin-1 and streptococcal pyrogenic exotoxin C, that lack CD40 binding. Specific aim 1b. To test wild-type SAgs and non-lethal mutants for ability to bind CD40 in immunoblots and Biacore analysis. Specific aim 1c. To test wild-type SAgs and dodecapeptide mutants for ability to penetrate porcine and rabbit vaginal mucosa. Specific aim 1d. To test non-lethal SAg mutants that retain mucosal penetration and CD40 binding for adjuvanticity, with the hypothesis that both activities result from mutant SAg interaction with CD40 on epithelial cells and APCs. Aim 2: To elucidate the contribution of staphylococcal SAgs to NP, pulmonary TSS, and endocarditis caused by emerging MRSA. We hypothesize that MRSA strains make higher levels of SAgs than MSSA strains, and that regulatory DNA controlling SAg production in MRSA is altered compared to MSSA. We also hypothesize that MRSA strains make high levels of SAgs required for NP, pulmonary TSS, and endocarditis, that alpha- hemolysin and Panton-Valentine leukocidin contribute to infections, but neither is required, and that SAgs contribute to infections by delaying antibody responses. These will be tested by use of isogenic strains, through vaccination, and by monitoring host responses. Specific aim 2a. In vitro characterization of emerging MRSA strains. Specific aim 2b. In vivo characterization of SAg contribution to CA-MRSA pulmonary infections. Specific aim 2c. Characterization of SAg contribution to MRSA endocarditis.